Can Mixer IP3 be Infinitely High?

We show a mixer circuit that exhibits infinitely high third-order intercept point (IP3) over a range of RF input levels. It follows from this fact that IP3 is not adequate for characterizing mixers. The formula for calculating IP3 from fundamental- and third-order intermodulation products at a single RF input level is not valid for the mentioned mixer over an RF input power range. Instead of IP3, we suggest a replacement.